This invention relates generally to bone stabilization implants, and more particularly to bone stabilization implants having a bone plate portion with integral cable clamping means.
In many bone stabilization procedures, particularly those involving elderly patients, it is necessary to attach a bone plate to the patient's bone in order to stabilize the bone, aid in mending a fracture and add strength to an otherwise weakened bone. Although it is usually most desirable to employ the use of bone screws to secure the plate to the patient's bone., it is sometimes necessary to utilize cable to secure the plate to the bone where bone screws, for one reason or another, are unsuitable or undesirable. Such a situation often occurs when obstacles are present or the bone has insufficient material to satisfactorily secure a bone screw or for one of a myriad of other reasons known in the art which render the use of cables more desirable than bone screws.
In one bone stabilization implant of the prior art, bands of metal are used to secure the bone plate portion to the bone. In another prior art bone stabilization implant, separate crimp sleeves are received in machined troughs made in the bone plate portion of the implant. Wire cable is then wrapped around the bone and its ends which are received in the crimp sleeves. In still another prior art bone stabilization implant, separate specially shaped grommets are received in the screw holes of the bone plate portion of the implant. The grommets include crimp sleeves which receive the ends of a cable being utilized to secure the implant to the bone. Unfortunately, all of these prior art devices suffer, to one extent or another, from problems associated with micro motion, unnecessary stressing of the cable or band and unnecessary weakening of the bone plate portion itself.
Micro motion has the potential to occur whenever two metal parts have the potential to move with respect to one another. This micro motion is very undesirable for several reasons: 1) Micro motion causes wear that releases metal fragments into the tissue of the patient potentially causing undesirable side effects; 2) the same wear produced by the micro motion tends to weaken the cable or band securing the bone plate to the bone creating the eventual likelihood of breakage; and 3) wear also tends to weaken the bone plate itself. Micro motion is primarily attributed to the fact that prior art devices utilize a separate crimping device that is held in place against the bone plate portion of the implant only by the tension in the cable or band. Any potential advancement in the art that would substantially eliminate the possibility of this micro motion would lessen the undesirable likelihood faced by many implant patients of having to undergo the second implant operation in order to repair or replace portions of a broken or weakened implant.
Although breakage in a cable can occur due to the micro motion discussed above, it is more often the result of unnecessary stresses on certain portions of the cable due to the structural contours of the assembled bone stabilization implant. In other words, the cable does not rest on a smooth continuous surface in prior art devices, instead the cable is highly stressed in locations where it must round relatively tight corners or otherwise come in contact with a protruding corner. Any advance in the art which aids in uniformly distributing the stress in the cable or band will also help to eliminate the likelihood that some implant patients will have to return to undergo a repair or replacement of their bone stabilization implant.
Another undesirable feature of certain prior art bone stabilization implants utilizing a trough to receive a crimp sleeve, is the fact that the bone plate portion is weakened in that area where a trough is located simply because of the reduction in thickness of the bone plate portion. In other words, a bone stabilization implant having troughs must be made thicker in order to provide the same strength as a bone plate portion having substantially uniform thickness.
Still another undesirable feature of prior art devices is the difficulty encountered when the device is actually implanted. These problems occur both because the prior art devices are more cumbersome to use due to the necessity of manipulating several small and separated crimp sleeves and grommets, as well as the difficulty of manipulating the bone plate portion itself into a desired position. This latter problem occurs primarily because prior art devices lack any good clamping surfaces which would allow a tool to grip the bone stabilization implant to aid in maneuvering it into position during an implant procedure. Prior art devices typically must be manipulated using extra hands and fingers crowding the implant area with attempts to grasp and hold the rounded surfaces typically prevalent on bone stabilization implants.
The present invention is directed to overcoming these and other problems associated with prior art bone stabilization implants.